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2. The role of bicarbonate in the activity of photosystem 2
- Creator:
- van Rensen, J. J. S.
- Format:
- Type:
- model:internalpart and TEXT
- Language:
- Multiple languages
- Description:
- Photosystem 2 (PS 2) reaction centre can be considered as a water-plastoqninone oxido-reductase. Using four photons it transfers four electrons from two molecules of water to plastoquinone (PQ), producing the molecular oxygen and two molecules of double reduced PQ. PS 2 is the site of the antagonistic action of bicarbonate and formáte on PS 2 electron flow; incubation of isolated chloroplasts with formáte results in full inhibition of electron flow actívity, which can be restored by addition of bicarbonate. This bicarbonate effect is located at the Dl protein and affects the electron flow between the primary quinone and the PQ pool. Bicarbonate is probably involved in stabilizatíon of tíie semireduced secondary quinone Qb, and in the protonation reactions at this site. Under physiological conditions bicarbonate is boimd to thylakoid membranes. Addition of formáte to thylakoids appears to release CO2. The bicarbonate effect is not only observed in isolated chloroplasts, but also in intact organisms as green algae and leaves. Bicarbonate Controls PS 2 electron flow in order to cope with stress conditions leading to, for instance, photoinhibition or to the high rates of photorespiration.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3. Ultrastructure and localisation of late-sporogonic developmental stages of Sphaerospora ranae (Myxosporea: Sphaerosporidae)
- Creator:
- Jirků, Miloslav and Bartošová-Sojková, Pavla
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- Amphibia, Anura, Europe, kidneys, myxospore, Myxozoa, Rana, sporogony, synchronisation, and in situ hybridisation
- Language:
- English
- Description:
- Data on external ultrastructure of myxospores and internal ultrastructure of advanced pseudoplasmodia and myxospores of topotypic samples of Sphaerospora ranae (Morelle, 1929) from Rana dalmatina Bonaparte are provided, together with in situ hybridisation results. In both frogs examined, the infection was restricted to renal tubules and corpuscles. The infection site restriction was confirmed by light and transmission electron microscopy, as well as by in situ hybridisation. In addition, large myxospore masses measuring up to 500 μm were detected in seminal vesicles. Only late-sporogonic stages, i.e. pseudoplasmodia harbouring immature and/or mature myxospores, were observed and analysed. Scanning electron microscopy revealed that spores have smooth surface with exception of posterior valvular bulges, which possess numerous outwards opening internal canals. As revealed by both scanning and transmission electron microscopy, the canals are continuous invaginations of the outer spore surface. Myxospores of S. ranae are characterised by the presence of two uninucleate sporoplasms, bilayered polar capsules, S/H-shaped polar filaments in transversal section and multilayered polar filament eversion pole plugging complex. Ultrastructural observations are discussed in the context of available data for other species of Sphaerospora sensu stricto and apparent synchronisation of myxospore shedding with a brief aquatic breeding phase of vertebrate intermediate host is highlighted.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public